1. Field of the Invention
This invention relates to computers with a pen or touch sensitive display, for example palmtop and notebook computers running a pen-enabled operating system.
2. Description of the Prior Art
In portable computer design, one typically wants to include a large display, yet keep the overall size of the computer as compact as possible. Successfully reconciling these two requirements is one of the more difficult problems facing the designer of portable computers. There are two well established solutions to this problem: Conventional portable computers, such as PDAs (Personal Digital Assistants), palmtops, sub-notebooks and notebooks, generally use either a tablet or a clam shell design. An example of a tablet design is the Apple Newton PDA from Apple Computers, Inc. In a tablet, the computer is a one-piece unit with a display occupying much of the upper surface. In the clam shell design, the display is usually hinged at or near the rear of the computer. The clam shell approach is used in the Psion Series 3a palmtop from Psion Computer PLC and virtually all sub-notebooks and notebooks. Both approaches enable a display that occupies much of the footprint of the device to be used.
The clam shell approach can bring its own problems: in early notebook designs (for example in the late 1980s), the display was far heavier than it is in today's machines. That was in large part because of the relatively thick glass used at that time and the type of display technology used. U.S. Pat. No. 4,960,256 to Sony Corporation from 1988 notes that some clam shell notebooks can tip backwards after the display has been opened up for viewing. That happens when a vertical line drawn through the center of gravity of the computer does not fall within the base of the computer but instead falls to the rear of and outside of the computer. The Sony patent teaches a hinge that enables the lower edge of the display to slide forwards when the display is opened up for viewing. Moving the base of the display forwards in this manner ensures that the center of gravity of the computer does not shift backwards when the display is fully opened so much that the computer tips backwards.
The Sony patent does not, however, relate to a computer with a pen or touch sensitive display. There are now however numerous PDAs with clam shell designs that include pen sensitive displays. These PDAs include the Philips Velo and various palmtops from Hewlett-Packard. One characteristic of these devices is that they use the Microsoft Windows CE (TM) operating system, which provides for pen input for selecting on-screen buttons, drop down windows, and electronic inking. However, a major design failing of these clam shell computers is that they topple over backwards if anything more than a very light pen touch, for example, 20 g-force, is applied to the display screen. In practice this requires the user to grasp the computer manually to prevent it toppling backwards.
Reference may also be made to U.S. Pat. No. 5,267,123 to EO Europe Limited. This discloses a notebook format light pen computer which, when closed, has the display upper-most. The display can be slid backwards to reveal a keyboard and can be inclined to a suitable viewing angle. Hence, it can operate as both a tablet (i.e. with the lid fully closed) and as a combination keyboard and light pen driven device. The display screen has a rear support which gives the display some rigidity with respect to the base of the computer: i.e. it prevents the display from moving back towards a horizontal position under pen pressure even when the base remains stable. Prior art such as the EO Limited patent relate to full sized laptops dating from 1990 and the base and display used in such a device would have been heavy. Hence, no specific design features appear to have been included in order to minimize the torque associated with pen or touch input to the screen below a threshold level.